(I think this counts as fictional biology.) There seems to be some dispute in nerd circles about the merits of two-legged dragons and four-legged dragons, and not being super well-read in fantasy, I'm wondering what people here think.

First of all, some people insist that the two-legged creatures aren't dragons at all and should be called wyverns, but I think this insistence is misguided. In the specific context of European heraldry, or within a fictional universe that contains both creatures, sure, it's okay to make that distinction. But the term dragon has seen a range of uses over the ages, and in antiquity, δρακων or draco generally referred to a large serpent or sea monster. And in our world it's certainly not uncommon for a name to be applied to more than one kind of animal. If a given universe contains only winged fire-breathing reptiles of a bipedal nature, it seems silly to say they're not dragons.

Now, my experience mostly comes from A Song of Ice and Fire, which contains two-legged dragons. On his blog, George R.R. Martin has said that he took his cue from the real world, in which all the larger winged creatures – bats, birds, pterosaurs – have had two legs, not four. He also pointed out that heraldry is a poor guide, since heraldic depictions of animals are infamous for their inaccuracy. (I was confused to find a reference to wyverns in one of his books, but he's clarified that wyvern, in his world, refers to a dragon-like creature that doesn't breathe fire. As long as he follows consistent rules in-universe, that's cool.) But in Tolkien's world, dragons such as Smaug have four legs, and there was some kerfuffle when he was changed from quadrupedal to bipedal midway through production of the most recent Hobbit movie.

So my questions are, which kind of dragon do you prefer, and which kind do you think is more plausible in a fictional biology context? My own preference, on both counts, is for two legs. The argument from nature seems to hold water: dragons seem more airworthy with two legs, and I think they look cooler and more threatening too. On the other hand, the dominance of the four-legged kind in European and Asian tradition, and in a lot of fantasy works, seems to make them the establishment choice – and I'll concede that they do look more physically imposing. Do the quadrupeds have some other virtues that I'm overlooking?